Calorimetry is a measurement technique used to measure the changes in heat of an isolated system. Differential scanning calorimetry applies an approximately linear temperature profile to an isolated system while a reaction occurs in one part of the system. Differences in temperature across the temperature scan provide information about the thermodynamics of the reaction. Microcalorimetry is a measurement technique based upon a small sized calorimeter and as a result is applicable to analyzing the reactions of small samples, for example, thin films. A microcalorimeter is able to measure the heat of reactions of thin films because of the small size of the instrument; in ordinary calorimeter ovens, the thin film is too insignificant in the device to gain any information about its chemical reaction.
A non-scanning, that is, constant temperature microcalorimeter device is described in U.S. Pat. No. 5,451,371. The device is built on a silicon base and the base is etched, leaving a frame of silicon supporting two suspended polysilicon platforms. A catalyst is used on one platform to sense the presence of hydrocarbons. Platinum resistors on each platform serve as heaters and thermometers.
An article entitled "Thin Film Microcalorimeter for Heat Capacity Measurements from 1.5 to 800 K", Denlinger et al., Review of Scientific Instruments, American Institute of Physics, 1994, describes a microcalorimeter fabricated from a silicon nitride membrane mounted in a silicon frame. The membrane provides a platform that contains a platinum heater, a thin film platinum thermometer for high temperatures, and a Nb--Si low-temperature thermometer. The device does not have separate sample and reference zones for accurate scanning measurements.
The prior art fails to adequately resolve issues of thermal isolation and measurement accuracy in scanning microcalorimeters. It is an object of this invention to provide a scanning microcalorimeter on a chip with good thermal isolation between sample and reference zones to enable the measurement of small samples and thin films or monolayer films over a large range of temperatures.